1. Field of the Invention
The present invention relates to liquid crystal displaying techniques, and in particular to a side-edge backlight module having non-uniformly sized backlight sections and a deign method thereof.
2. The Related Arts
The fast development of LED television is now getting into a new era of 3D liquid crystal television. Among the 3D liquid crystal televisions, one of the most commonly used techniques is the shutter glasses 3D displaying technique, in which separate display of signals for left and right eyes is done with sectionalized illumination of backlighting and is used in combination with synchronous flashing of eyeglasses to make the left and right eyes perceiving different images. The shutter glasses 3D displaying technique applies image processing technology to provide a visual effect to human eyes that looks like a stereoscopic movie, which generally comprises alternately supplying signals of left-eye frames and right-eye frames to a liquid crystal panel in order to drive the liquid crystal panel to separately form left-eye images and right-eye images. This, when combined with illumination of a scanning backlight unit and timing control of the shutter glasses, allows the left-eye signals and the right-eye signals to respectively simulate the left eye and the right eye, making a person perceive a 3D image.
However, the 3D liquid crystal display devices have a drawback that since the liquid crystal panel does not emit light by itself, backlighting must be provided to serve as a light source. Due to the consideration of cost factor, sectionalization of the backlight cannot be made very fine. As shown in FIG. 1, a schematic view showing sectionalized lighting and light leakage of a conventional side-edge LED backlight is given. The side-edge LED backlight comprises LED chips that are arranged along circumferential edges of a liquid crystal panel and a light guide plate is included to allow the LED backlight to be lit in a sectionalized manner for conducting light emitting from the circumferential edges of the liquid crystal display panel through the light guide plate to reach a central zone of the liquid crystal display panel. This provides sufficient backlighting entirely, allowing the liquid crystal display panel to display images. The side-edge LED backlight has two advantages. One is that less LED chips can be used and cost is lowered down. The other is that it is possible to make a device body thin by not arranging LED modules on the back side of the liquid crystal panel of LED television but at lateral sides so as to reduce the overall thickness of the liquid crystal panel and thus make the device body extremely thin.
FIG. 1 shows a backlighting section 11 that is of light incidence at a right side short edge. Asymmetry of light leakage is because leakage gets severer with the longer light path. When the backlighting section 11 is lit, light leaks to the sections 12 and 13 on the opposite sides thereof and this causes interference between left-eye and right-eye signals. In other words, the left eye may perceive the signal for the right eye (or the right eye sees the signal for the left eye) and this makes image blurred (for the two signals show distributions that overlap in space). The criterion for assessing image blurring is cross-talking, of which a higher value indicates severer interference. Thus, it is an important issue to reduce cross-talking while maintaining price competitiveness for products.
The cross-talking occurring between a left-eye signal and a right-eye signal of the conventional shutter glasses 3D displaying technique is determined by the technical nature thereof. The backlight module of the conventional shutter glasses liquid crystal 3D display is arranged to form an even number of backlighting sections by dividing a horizontal block in a vertical direction and scanning is carried out from top to bottom to sequentially control activation and operation time for each backlighting section of the backlight module. Image signals (left-eye signals and right-eye signals) sequentially supply, from top to bottom, driving voltages to each row of the liquid crystal panel. Only after pixels receive and are charged by the driving voltages, the liquid crystal panel starts to respond. Due to the design of pixel and the viscosity of liquid crystal, a complete steady state can only be reached after a period of liquid crystal response time. Since liquid crystal responds slowly, image signals are displayed on a liquid crystal panel in a sectionalized scanning fashion. When an image signal scans one of the sections of the liquid crystal panel, the corresponding section of backlight will be set on and the remaining backlight sections are off. Since leakage exists in the backlight sections, when light leaking from a backlight section corresponding to a left-eye signal irradiates a backlight section corresponding to a right-eye signal (or when light leaking from a backlight section corresponding to a right-eye signal irradiates a backlight section corresponding to a left-eye signal), the eyes will simultaneously perceive the left-eye image and the right-eye image, causing cross-talking. The right-eye signal or the left-eye signal that causes cross-talking will be referred to as an error signal (or interference signal).
As shown in FIGS. 2A and 2B, schematic views illustrating sectionalized lighting of backlight for a 46-inch single short edge side-edge LED television are given. Taking the 46-inch single short edge side-edge LED television as an example, the backlight module 20 is often divided into an even number backlight sections, such as four sections, for sectionalized lighting. An edge side backlight section 21, once lit, leaks toward the middle, while a middle backlight section 22, once lit, leaks toward opposite sides.
As shown in FIG. 3, a schematic view showing nine points on a liquid crystal panel where cross-talking is measured. In FIG. 3, a display screen 30 has adjacent sizes of which the dimensions are respectively denoted by reference symbols H and V. The nine points, namely point 1, point 2, . . . , and point 9, are arranged according to the relative positioning relationship as shown in FIG. 3. The locations of point 1, point 2, . . . , and point 9 on the display screen are exactly the locations on the liquid crystal panel. Measurements are made on a conventional LED television with 46-inch single short edge incidence and four backlight section scanning and the detected cross-talks at the nine points of point 1, point 2, . . . , and point 9 are listed in the following Table 1, which clearly indicates that the cross-talking shows a characteristic of vertical asymmetry, with the upper side being much severer than the lower side. In addition, these cross-talks also show horizontal asymmetry. This is caused by the single short edge incidence, where the further the optic path goes, the severer the leakage will be
TABLE 1Cross-Talks Measured at Nine Points (46″ single short side incidenceand four backlight section scanning)single short edge incidenceLeft 1/9Middle 1/2Right 8/9Upper 1/914.99% 8.84%7.03%Middle 1/25.60%4.51%3.69%Lower 8/98.47%6.20%4.81%
Due to the arrangement of backlight sections, timing coordination among liquid crystal panel signals, glasses signals, and backlight scanning often result in asymmetry of cross-talking. The data of Table 1 reveal that for a conventional 46-inch single short edge side-edge LED television, the left-eye signal or the right-eye signal shows an image of the best quality on the middle portion of the liquid crystal panel and the quality of image displayed on the liquid crystal panel is generally unsymmetrical in the vertical direction. The vertical asymmetry of cross-talking shown in Table 1 can be explained with the timing relationship between the backlight sections and the liquid crystal panel signals.
As shown in FIG. 4, a schematic view is given to illustrate the timing relationship (a left-eye signal being used for demonstration) between the backlight sections of a conventional 46-inch single short edge side-edge LED television and the liquid crystal panel signals (the left-eye image and the right-eye image signal applied to the liquid crystal panel). The backlight module is divided, sequentially from top to bottom, into a first backlight section 41, a second backlight section 42, a third backlight section 43, and a fourth backlight section 44, which respectively function to illuminate first, second, third, and fourth display sections of a liquid crystal panel 40. In FIG. 4, a left-eye signal is taken as an example for demonstrating four successive steps of the operations of the liquid crystal panel 40 and the backlight module for displaying liquid crystal panel signals: step a, in which the first to third display sections are loaded with a left-eye signal of the current frame and the fourth display section is loaded with a right-eye signal of the previous frame; the first backlight section 41 is lit to illuminate the first display section and since leakage from the first backlight section 41 might undesirably illuminate the fourth display section, the right-eye signal of the previous frame loaded in the fourth display section becomes an error signal of cross-talking with the left-eye signal of the current frame loaded in the first display section; since the first display section and the fourth display section are spaced from each other by two display sections therebetween and the distance is great, the cross-talking so caused is minor; step b, in which the fourth display section is also loaded with the left-eye signal of the current frame so that at this moment, the liquid crystal panel 40 is entirely loaded with the left-eye signal; the second backlight section 42 is lit to illuminate the second display section; at this moment, leakage from the second backlight section 42 does not cause cross-talking between the left-eye signal and the right-eye signal, providing the best image quality; step c, in which the first display section is loaded with a right-eye signal of the next frame and the second to fourth display sections are loaded with the left-eye signal of the current frame; the third backlight section 43 is lit to illuminate the third display section; at this moment, the right-eye signal of the next frame loaded in the first display section becomes an error signal of cross-talking with the left-eye signal of the current frame loaded in the third display section; since the first display section and the third display section are only spaced by one display section therebetween and the distance is short, the cross-talking is severe; and step d, in which the first and second display sections are loaded with the right-eye signal of the next frame and the third and fourth display sections are loaded with the left-eye signal of the current frame; the fourth backlight section 44 is lit to illuminate the fourth display section; at this moment, the right-eye signal of the next frame loaded in the first and second display sections becomes an error of cross-talking with the left-eye signal of the current frame loaded in the fourth display section; since the first and second display sections are spaced from the fourth display section by only one display section therebetween and the distance is short, the cross-talking is severe. The severeness of cross-talking is different when different backlight section is lit. During the entire process of 3D displaying, the liquid crystal panel 40 repeats the processes of loading a right-eye signal (the previous frame), loading a left-eye signal (the current frame), loading a right-eye signal (the next frame), loading a left-eye signal, loading a right-eye signal, and so on. Since the conventional side-edge backlight sections are set up for sections of even number, when an error signal appears, the influence it imposes on the upper and lower sides is different. In this example, the error signal generated when a backlight section is lit is closer to the upper side and the upper side cross-talking is severe in the liquid crystal panel 40 so that the cross-talking of the liquid crystal panel 40 is unsymmetrical in the vertical direction. Adjustment may be directly made on the liquid crystal panel signal to make backlight section lit at a center of the liquid crystal panel signal. Although the cross-talking of the liquid crystal panel 40 can be made substantially symmetric in the vertical direction, yet due to the number of the backlight sections being even, the quality of image at the center position will be sacrificed and cross-talking gets serious.